I have never seen shingle granule loss to this extent, the owner told me the roof was about ten years old.

This appears to be excessive granule loss. Near uniform loss across the shingles indicates that it's not foot traffic, in which granule loss would be concentrated on the butts. Uniformity of granule loss indicates pressure washing from the ridge toward the eaves.

For comparison:

The first photo is from foot traffic. Poor resistance, probably a manufacturing defect. No claim was ever filed so we don't know.
The second is an example of damage that appears to be from pressure washing.
You can express an opinion, but either you know or you don't.
Luckily, we are not required to determine the cause of problems, only to identify that one exists and make a recommendation.

In this case mine would be:
1. If the roof were still under warranty, examination by a manufacturer's representative.
2. If not, the roof appears to have suffered functional damage that increases the chances of leakage.